1. Field of the Invention
The present invention relates to an image pickup apparatus and an imaging method, and more particularly to a technique related to automatic focusing (AF) used in a digital still camera, a digital video camera, and the like.
2. Description of the Related Art
Conventional automatic focusing apparatuses mainly use a method for controlling a focusing lens position to maximize an automatic focusing (AF) evaluation value for focus adjustment. The AF evaluation value is obtained by photoelectrically converting an object image into a video signal by an image sensor and detecting screen sharpness from the video signal.
The level of a high-frequency component of the video signal extracted by a band-pass filter having a certain band is usually used as the AF evaluation value. When capturing a normal object image, the level of the AF evaluation value increases as the object image comes into focus. A point that maximizes the level is an in-focus position.
If the captured scene does not change, the focusing lens is subsequently stopped to enter a state of monitoring the AF evaluation value and brightness (hereinafter, a monitoring state). In the monitoring state, the AF evaluation value is calculated based on the video signal. If an object leaves or enters the screen, the AF evaluation value thus changes and it is determined that the scene has changed. As a result, the automatic focusing apparatus may come into an operation for searching for an in-focus position (Japanese Patent Application Laid-Open No. 2014-38197).
Performing a focus adjustment by using a plurality of different focus adjustment methods, such as a minute driving operation and a hill-climbing operation, is known.
The minute driving operation is an operation for reciprocating the focusing lens by a unit movement amount smaller than a predetermined value in an intermittent manner to obtain an AF evaluation value, and controlling the focusing lens in a direction in which the AF evaluation value increases.
The hill-climbing operation is an operation for obtaining AF evaluation values while moving the focusing lens in a specific direction in a unit movement amount greater than the predetermined value, and identifying an in-focus position from the configuration of the plurality of AF evaluation values.
If there is a scene change as described above, the minute driving operation is initially performed to identify an in-focus position and a direction of the in-focus position.
However, suppose that an object moves out of the screen during the identification of the in-focus position. If the background contrast is low, it takes a long time to identify the in-focus position and the direction thereof since a change in the AF evaluation value is difficult to detect.
In such a case, the minute driving operation transitions to the hill-climbing operation along the way to search a wider range for an in-focus position. However, as a result of the foregoing determination of a scene change, the focusing lens may stop at a position other than an originally expected in-focus position. Or tracking to the in-focus position may become unstable and visually undesirable.